1. Field of the Invention
The present invention relates generally to a transmission device for transmitting the torque of an engine to an output device, and particularly to a transmission device adopted for a working tool such as a weed cutter having an engine, a rotary blade, and a gear case for supporting the rotary blade rotatably, wherein the transmission device comprises an operation pipe for connecting the gear case with the engine and a transmission shaft disposed inside the operation pipe to transmit the engine torque to the rotary blade via the gear case. As another feature of the present invention, the transmission device comprises a vibration isolator interposed between the operation pipe and a clutch housing of the engine.
2. Description of the Prior Art
FIG. 1 shows a transmission device according to a prior art. This transmission device may be adopted for a weed cutter which is generally shown in FIG. 2. This prior art transmission device comprises an operation pipe 7 for connecting an engine 5 with a rotary blade 1 through a gear case 3, a transmission shaft 15 disposed inside the operation pipe 7, and a bearing pipe 9 also disposed inside the operation pipe 7 to surround and support the transmission shaft 15 rotatably. The bearing pipe 9 is disposed coaxially inside the operation pipe 7 to continuously support the total length of the transmission shaft 15.
In such a bearing structure, the contacting area between the outer surface of the transmission shaft 15 and the inner surface of the bearing pipe 9 is large so that the frictional resistance between them will excessively be large to increase the transmission loss of torque. As a result, the deterioration of acceleration capability, the lack of revolution speed in a high-speed range, and the excessive heating of the operation pipe due to the frictional heating may be caused in the weed cutter provided with such a prior art transmission device.
FIG. 1(B) is a view showing a vibration isolating connection between the operation pipe 7 and a clutch housing of the engine 5 according to the prior art. In the figure, a vibration isolator 201 made of rubber, etc., for preventing vibrations generated by the engine 5 from propagating to the operation pipe 7 is fixed by heat sealing or adhesion to the periphery of an inner cylinder 203. The inner cylinder 203 has grooves 205 and is engaged with an end of the operation pipe 7. After the engagement, the inner cylinder 203 is tightened by a clamp 207 at the grooves 205 such that the inner cylinder 203 is fixed to the operation pipe 7. The periphery of the vibration isolator 201 is provided with projections 209 formed in an axial direction to removably engage with grooves 211 formed in an axial direction on a cylindrical portion 213 of a clutch housing 215 of the engine 5.
According to this arrangement of the prior art, there are many parts to be assembled for constituting the vibration isolating connection between the operation pipe 7 and the clutch housing 215 of the engine 5 so that the assembling work may be bothersome, and the total weight increased.